The corpus luteum is the principal source of progesterone, which is essential for nidation and maintenance of early pregnancy in women. Adequate corpus luteum function is dependent upon both pre-ovulatory follicular development and a balance between luteotrophic and luteolytic factors. FSH is essential for ovarian follicular recruitment and maturation. The major luteotrophic factor appears to be gonadotropins, primarily LH. Prolactin appears to have effects on the corpus luteum as well. We now appreciate that the dominant mode of gonadotropin and prolactin secretion is pulsatile in nature. The pulsatile pattern of gonadotropins changes throughout the menstrual cycle. The physiologic significance of the gonadotropin secretion pattern on ovarian function, follicle development, and the corpus luteum in particular is not well understood. Luteal phase deficiency (LPD) is primarily a problem of inadequate post-ovulatory progesterone production by the corpus luteum. We have described abnormalities in the gonadotropin pulse pattern in women with LPD. Although LPD has been clearly described in the research setting, the prevalence and significance of LPD in clinical reproductive medicine remains controversial. The clinical controversy stems from the use of several diagnostic methods that have not been completely substantiated and the lack of controlled therapeutic trials. LPD, in the context of a biologic rather than a clinical phenomenon, presents a useful model for the study of corpus luteum function. The objective of this proposed research is to investigate corpus luteum function in relation to gonadotropin and prolactin secretion. First, we will examine the effects of accelerating the luteal gonadotropin pulsatile rate on corpus luteum function and subsequent follicular development in normal women. Second, we will accelerate the follicular gonadotropin pulse rate with exogenous LHRH in normal women in order to study the effects on corpus luteum function and see whether we can induce LPD. Third, we will critically assess the diagnostic methodology for LPD and characterize the gonadotropin and prolactin pulse pattern in women with LPD.